The invention relates generally to apparatus for electrically stunning animals to be slaughtered, such as pigs, sheep, cattle, and other animals which are slaughtered to produce meat usually for human consumption.
Before animals such as pigs are slaughtered, they should be rendered unconscious, or stunned. Stunning the animals before slaughtering helps to prevent unnecessary animal suffering. Such stunning is desirably accomplished by applying an electrical shock to the animal. To render the animal unconscious, it is desirable to pass sufficient electrical current through the animal's brain to result in a generalized epileptic insult. In the past, the electrical shock has been induced by manually applying electrodes to the animal. There has been a need in the art for an apparatus that can effectively stun animals automatically without requiring manual placement of the electrodes.
In the past, manual methods have included utilization of a pair of electrical contacts, or stunning rods, which are held by a human operator against the head of an animal so that electrical current flows from one electrical contact through the animal and to the other electrical contact. The stunning rods may be applied in a longitudinal direction, relative to the animal's body, or in a direction transverse thereto.
Manual stunning techniques have been plagued with problems, such as, the improper application of electrodes to the animal, insufficient current flow to effectively render the animal unconscious, the failure to immediately evoke unconsciousness, the failure to prevent unnecessary animal suffering, and the failure to adequately protect the safety of stunning equipment operators.
70 volts is a commonly used voltage for manual stunning methods. If a human equipment operator is to handle the electrodes used for stunning, it is desirable to keep the voltage as low as possible to minimize the danger of electrocution to which the operator is exposed. In practice, it has been found that while 70 volts may immobilize a pig's neuromotor functions, electro-encephalographic traces showing the pig's brain activity have revealed that a pig remains conscious after being stunned with only 70 volts. Such insufficient stunning is cruel and causes unnecessary animal suffering.
In pigs, it has been found that the current level generally necessary to achieve an immediate effective stunning in at least 90% of the pigs tested was 1.07 ampheres. In practice, it has been found that 70 volt equipment fails to produce current levels of 1.07 ampheres in a pig. Increasing the voltage to a more dangerous level of 180 volts will sometimes produce a current level greater than or equal to 1.07 ampheres, and sometimes will not produce the necessary current level.
The current flow required for stunning should pass directly through the head of the animal at the correct potential and the correct intensity. It must pass through the head so that current will flow through the animal's brain, instead of through the animal's muscle tissue. It must be at the correct potential and intensity to insure that the animal is rendered unconscious, not just merely immobilized.
Voltage levels as high as 300 volts and 525 volts have been used in the past. However, the use of such voltage levels creates problems. As the voltage is increased, the danger to human equipment operators is increased. It is undesirable to force a man to handle electrodes with such high voltages present on the electrodes.
Also, when the voltage level is as high as 300 volts or 525 volts, if the electrodes are applied to the animal so that significant current flows through the animal's muscles instead of its brain, severe muscle contractions can be induced in the animal. The muscle contractions can be so severe that bone breakage and internal bleeding can occur.
Such severe muscle contractions cause unnecessary animal suffering. In addition, improper current flow during stunning should be avoided because it can result in reducing the value of the meat of the animal to be slaughtered. When muscular contractions occur in the animal, causing bone breakage and internal bleeding, the meat of the animal must usually then be classified as a lower quality or grade of meat.
High voltage current flowing through muscle tissue causes adverse consequences including unfavorable post-mortem chemistry in the animal meat. Such current flow through muscle tissue is believed to result in the release of lactic acid in the meat tissue because of the severe muscle contractions. The lactic acid accumulation may have an unfavorable effect on the quality of the meat and can result in a condition commonly referred to in the art as pale-soft-exudative, of P.S.E. The meat will have a poor color and appearance.
As the voltage level is increased the placement of the electrodes becomes more critical in order to avoid high voltage current flow through the animal's muscle tissue. Manual stunning methods have an element of uncertainty due to the manual application of the electrodes.
At low production rates, manual stunning techniques may result in a low percentage of animals that are not of prime quality due to internal bleeding and bone breakage caused by the improper application of electrodes. Manual stunning presents, however, the drawback of limited production, because human operators in practice have not generally been capable of production rates above a certain level of production without adverse effects on efficiency. Attempts to increase the production rate can result in a significant increase in the incidence of misapplication of the electrodes to animals. Furthermore, to avoid the situation where the animal to be stunned only loses consciousness momentarily, it is desirable to use a high voltage which is believed to adversely affect the human operator's safety.
For example, if a production rate of 600 pigs an hour were to be attempted, the human operator would have to stun an animal every six seconds. This would create a great deal of stress upon a human operator, who must handle high voltage electrodes and quickly apply them to each animal's head while the animal may be squirming or trying to avoid the electrodes. In practice, it has been found that the number of times that a human operator will improperly apply the electrodes, inducing convulsions and resulting in low grade meat, increases substantially at such attempted production levels. In other words, a higher drop out percentage results.
In the past, attempts to develop an automatic stunning apparatus resulted in a higher drop out percentage than that occurring from manual stunning even at slow production rates. That is, a greater percentage of lower quality grade meat was obtained from animals subjected to such attempts at automatic stunning as compared to manual stunning. There has been a long felt need in the art for an effective automatic stunning apparatus.
U.S. Pat. No. 1,857,658, issued to Pfretzschner, represents an attempt at an automatic stunning device. The flaps illustrated for use as electrodes are intended to roll over the back or sides of the animal to be stunned. Such a haphazard placement of electrodes would likely result in violent convulsions and broken bones, with the resultant adverse effects on meat quality.
It is important that animals be restrained during stunning so that the animals are not touching each other. If one animal is touching another animal that is being stunned, that animal will also receive a shock. Typically, the shock flows through muscle tissues and can cause convulsions, creating the adverse consequences that result from such convulsions, including broken bones, internal bleeding, poor meat quality, and unnecessary animal suffering. The previously mentioned Pfretzschner reference does not recognize this problem.
The present invention is believed to provide an automatic apparatus for electrically stunning animals in which the drop out percentage is equal to or less than that achieved with manual stunning techniques. The present invention is believed to provide an automatic apparatus capable of achieving production rates faster than are practicable with manual stunning.